A defiant Ms Mirabella stood by her comments when quizzed over their appropriateness, but Mr Swan says it is unacceptable for politicians to be making such comparisons.

"I have been surprised and then subsequently appalled by what appears to be a very deliberate strategy from the Liberal Party frontbench to compare ministers and the Prime Minister to terrorists and murderous dictators," he said.

The Treasurer says the comments are symptomatic of a trend within the Coalition, which he fears is following the path of conservative US politicians.

"The sort of images they are using are outrageous and I think they are dangerous for our country," he said.

"There's been a debate about this in the United States. I don't want to see us go down that road. I don't want to be here talking about these things, and they should desist."

Vitriolic debate

The standard of political debate has been in the spotlight after independent MP Tony Windsor released a threatening message that had been left on his phone.

"You're a f...ing liar, a dog, a rat, a big f...ing MP dog... and you wait. You're not going to get voted in again. I hope you die, you bastard," the caller said.

Mr Windsor says talkback radio hosts and politicians are feeding anger in the community that could lead to a tragedy similar to the recent shooting of a US congresswoman.

"I think the shock jocks and others are involved in an orchestrated campaign over the issue itself, but particularly they're targeting members of Parliament that want to be involved in the substantive debates," he said.

"I think if they keep running that line they may well have a self-fulfilling prophecy and incite people to do things they would never normally do."

Greens leader Bob Brown also says he has also received death threats over his party's push for a carbon tax.

"I've been on the receiving end of that - including recently," he said.

"Because of the debate about climate change and carbon tax, occasionally people get fired up and as a result of that we see that sort of unacceptable and inherently violent behaviour."

But while Opposition Leader Tony Abbott says Ms Mirabella's words are not language he would use, he has refused to condemn the comments.

"I think people understand in a robust democracy there'll be a lot of colourful language used," he said.

"But in the end, we are a democracy. We do respect each other and it's important that we convey our anger and our rejection of this new tax in appropriate ways."